With advance and progress of portable information devices such as mobile phones and digital cameras, there have been desired alkaline dry batteries capable of highly loaded discharge.
With regard to this, in conventional alkaline dry batteries, a particle size of a zinc powder contained in a gel negative electrode has been made small for improving highly loaded discharge performance. Specifically in practice has been to increase the amount of the zinc particles having a small particle size in the particle size distribution of the zinc powder. This is aimed at improving the reaction efficiency of the negative electrode attributed to the large specific surface area of the zinc particles having a small particle size.
However, there is a problem in such improvement of the reaction efficiency by immoderately reducing the particle size of the zinc powder, that in a case where a battery is short-circuited, the surface temperature of the battery rises and thereby the amount of gas generated inside the battery increases, resulting in the higher possibility of electrolyte leakage outside of the battery.
That is to say, in the conventional technique, it has been relatively difficult to realize both improvement of discharge performance by reducing the particle size of the zinc powder and safety maintenance, in a balanced manner.
Also in the conventional alkaline dry battery, as a negative electrode active material used has been a zinc powder including 90% or more of zinc particles having a relatively large particle size of 75 to 425 μm, and as a separator used has been one having a thickness of about 300 μm.
As described above, however, there has been a demand for alkaline dry batteries capable of highly loaded discharge and having long cycle life, with recent advance and progress of portable information devices such as mobile phones.
In response to this demand, studies have been made on reduction in thickness of the separator for lowering the resistance of the separator so as to improve the highly loaded discharge performance.
However, there has been a problem, in reduction in thickness of the separator with the use of the conventional zinc powder having a large particle size, that an internal short circuit may occur in the battery in such highly loaded discharge as 3.9 Ω for 5 minutes/day. This is because the zinc powder is oxidized corresponding to the battery reaction and the crystals of zinc grow to be acicular, which penetrate the separator to cause the internal short circuit.
On the other hand, another effort to improve the highly loaded discharge performance has been made by increasing a proportion of a zinc powder having a small particle size to be used as a negative electrode active material. It has been revealed, in this effort, that an increase in proportion of the zinc powder having a small particle size allows effective suppression of the internal short circuit of the battery.
Then, a first object of the present invention is to provide an alkaline dry battery low in the possibility of electrolyte leakage and excellent in discharge performance. Further, a second object of the present invention is to provide an alkaline dry battery which is unlikely to cause an internal short circuit even with reduction in thickness of the separator, by leading to a favorable relation between the particle size of the zinc powder and the thickness of the separator.